This invention relates to tire building drums and particularly to a drum which is adjustable in width for use in the manufacture of tires of different widths employing the same drum.
In the manufacture of vehicle tires, it is common practice to build up the tire carcass from individual components which are overlaid onto the outer circumference of a rotatable drum. Removal of the formed tire carcass from the drum requires collapse of the diameter of the drum to an extent sufficient to allow the toroidal carcass to be removed from the drum. U.S. Pat. No. 4,636,277 (the xe2x80x9c277 patentxe2x80x9d) discloses a tire building drum of this type. This prior art drum is also representative of prior art drums wherein any change in the width of the drum requires physical exchange of spaces between the outer shell segments which define the outer circumference of the drum to that size required for the manufacture of a given tire width size. This process is well known in the art to be cumbersome, time-consuming and expensive, and requires the keeping of an inventory of spacers.
Functionally, the drum of the xe2x80x9c277 patentxe2x80x9d requires special structure, and orientation of such structure, to successfully and repeated effect proper mating of the axially aligned side edges of adjacent ones of the segments to define a suitable working outer circumferential surface of the drum. Specifically, with reference to FIGS. 1 and 2 of the xe2x80x9c277 patentxe2x80x9d, it will be noted that the inboard ends of alternating ones of the radial support structures 14 are mounted on the rotating hub 11 at respective locations which are offset from a radius drawn from the central axis of the drum through the center of the outboard end of a given radial support 14. These offset alignments of the radial support members permits the smaller segments to move radially inwardly of the drum in advance of the radially inward movement of the larger segments as is required to permit collapse of the segments toward the rotational axis of the drum. This mechanism further causes the larger segments to move radially outward of the drum in advance of the movement of the smaller segments radially outwardly of the drum when expanding the diameter of the drum. However, this mechanism causes the larger segments to move radially beyond their desired most radially outward positions and then to move radially inwardly to mate with the advancing smaller segments. Control over the precise mating of the larger and smaller segments at their desired outer limit of travel has proven to be difficult to control. As a consequence addition of an adjustable stop mechanism has been employed to improve the desired stop positions of the mating side edges of the larger and smaller segments. This stop mechanism, however, must be fixedly mounted, preferably welded, in place adjacent each of the opposite side edges of the smaller segments before assembly of the drum, and its stop limit adjusted after assembly of the drum. This mechanism provides only for a xe2x80x9csingle pointxe2x80x9d adjustment of the position of the side edge of a larger segment relative to a cantilevered extension of the smaller segment. Accordingly, this mechanism represents an undesirable added cost in time and constitutes a point of potential need for ongoing adjustment over the useful life of a drum.
It is therefore an object of the present invention to provide a tire building drum which is expansible in diameter and selectively changeable in both its diameter and its axial width without exchange of the outer segments that collectively define the outer circumferential surface of the drum or the use of spacers.
It is another object to provide a drum of the type described in which the adjustment of the width of the drum may be effected from a location external of the drum.
As is another object to provide a radially expansible tire building drum having improved control over the mating of its circumference-defining segments